JPH0119501Y2 - - Google Patents

Description

[Detailed Description of the Invention] Technical Field of the Invention The present invention relates to a high frequency signal switching device in a CATV converter.

Conventional technology and problems In CATV systems, multiple high-frequency cables are installed to increase transmission capacity.
The CATV converter switches high-frequency cables, and the receiver switches channels to receive images. For example, as shown in FIG. 1, CATV cables 1 and 2 are laid, connected to a CATV converter 7 through lead-in taps 3 and 4 through lead-in cables 5 and 6, and a switching device inside the CATV converter 7 is used to connect the CATV cables 1 and 2 to the CATV converter 7.
2, the receiver 8 performs channel selection and receives the image.

In addition, paid CATV systems generally use a signal format that cannot be properly received by a normal TV receiver, so demodulation is required to ensure that only the subscribed channels can be properly received. A device (discrambler) is provided. In order to change or check the contents of the contract, the operation of the demodulator is changed by transmitting an address signal or the like. For example, as shown in FIG. 2, the CATV converter selects the aforementioned CATV cables 1 and 2 using a changeover switch 11 that selects the lead-in cable terminals 9 and 10, and selects the frequency from the signal input via the connection cable 12. A selection device 13 selects a receiving channel, a demodulator 14 processes the signal for normal screen reproduction, and the signal is sent from an output terminal 18 to a receiver. Further, the address signal of a predetermined frequency transmitted from the CATV cable 1 to the lead-in cable terminal 9 is transmitted to the lead-in tap 15.
and is applied to the address signal control device 17 via the connection cable 16, and from this address signal control device 17, a control signal for the demodulator 14 is applied, and the signal is processed by the demodulator 14 so that only the contract channel can be normally received. will be held. Further, in the case of changing the contracted channel, etc., the address signal control device 17 performs control to change the signal processing of the demodulator 14 based on the address signal.

FIG. 3 is an explanatory diagram of the aforementioned changeover switch 11 and retraction tap 15, and the changeover switch 11 is composed of a relay that performs a switching operation between the retraction cable terminals 9 and 10 by energizing an excitation coil 23. ing. Also a coupling capacitor 19,
22, a tuning capacitor 20 and a tuning coil 21 constitute a pull-in tap 15, and the signal selected by the changeover switch 11 is inputted to the demodulator 14 described above via the connection cable 12, and the predetermined frequency branched at the pull-in tap 15 is output. The address signal is input to the aforementioned address signal control device 17 via the connection cable 16.

For example, if the address signal has a center frequency of 106,
CATV transmitted at 5MHz, frequency deviation ±75KHz
In the system, coupling capacitors 19, 22
A very small capacitance of about 1 pF is used to minimize the effect on transmission characteristics other than address signals. Also, in order to make the tuning circuit resonate at 106.5MHz, for example, a tuning capacitor 20 of approximately 20pF is connected.
A tuning coil 21 of 112 nH is used.

FIG. 4 is a schematic perspective view of the circuit configuration shown in FIG. 3 formed on a printed circuit board, in which the capacitor 19,
20 and 22 are connected to a wiring conductor 26 formed on an insulating substrate 27. Further, the lead-in cable terminal 9 is connected to the connector 24, the lead-in cable terminal 10 and the connector 25, and connected to a relay (not shown) constituting the changeover switch 11 via wiring. Further, the tuning coil 21 and the connection cable 16 to the address signal control device 17 are not shown.

Figure 5 is an equivalent circuit of the lead-in tap section, and the wiring conductor 26 in Figure 4 is represented as floating inductances 28, 29, 30, connected between the coupling capacitors 19, 22 and the tuning circuit. becomes.

In a CATV converter, a wide frequency band (e.g. 50MHz to 500MHz) is connected to an empty channel (e.g.
60MHz), the first intermediate frequency is selected to be a higher frequency than the receiving frequency (for example, 600MHz), and in this case, the first local oscillation frequency is (50 + 600) ~ (500 + 600) = 650 ~ It becomes 1100 [MHz]. If the second local oscillation frequency is selected to be 660MHz, the output frequency will be 660-600=60 [MHz], which can be converted to an empty channel.

As described above, since the CATV converter has a built-in local oscillator for the UHF band, there is a high possibility that unnecessary signals will leak, and the leaked signals will interfere with other receivers via the cable. In particular, as shown in FIG. 5, there is a possibility that the stray inductance resonates with the tuning capacitor 20, causing a state in which signals in the UHF band are passed. Therefore, conventionally, in the configuration of the retracting tap shown in FIG. 4, UHF signals such as local oscillation signals induced in the connecting cable 16 etc. leak to the retracting cable via the connector 24 without attenuation. This may cause interference to other receivers. Furthermore, although the connection is made by a small capacitance, since the tap is connected in the middle of the TV signal transmission path, the standing wave ratio of the switching device deteriorates, causing a drop in matching characteristics. Therefore, the connection between the connector 24 and the relay constituting the changeover switch 11 needs to be arranged as short as possible.

As mentioned above, the high frequency signal switching device in conventional CATV converters has the drawback that local oscillation signals such as those in the UHF band leak to the lead-in cable terminal, causing interference to other receivers. This had the drawback of deteriorating the standing wave ratio of the switching device.

Purpose of the Invention The present invention aims to eliminate the conventional drawbacks as described above, prevent leakage of local oscillation signals, and improve matching characteristics.

Structure of the invention The present invention connects a tuning capacitor and a tuning coil that constitute a tuning circuit between a wiring conductor and a ground conductor formed on an insulating substrate, and connects a first and second coupling via the wiring conductor. connecting one end of the capacitor to the tuning circuit in close proximity to the tuning capacitor;
A specific high frequency cable is connected to the other end of the first coupling capacitor via a first matching inductance, and is connected to a switching switch via a second matching inductance, and the other end of the second coupling capacitor is connected to the other end of the second coupling capacitor. is connected to a connection cable that branches and outputs signals of a predetermined frequency. Examples will be described in detail below.

Embodiment of the invention FIG. 6 is a schematic perspective view of an embodiment of the invention,
The same symbols as in FIG. 4 indicate the same parts, 31 and 32 are matching inductances, and 33 is a relay (not shown) that constitutes the changeover switch 11.
Terminal 34 is the connection cable 16 for connecting to
(not shown), and 35 is a terminal for connecting to the tuning coil 21 (not shown). The coupling capacitors 19, 22 and the tuning capacitor 20 are arranged in close proximity, and a first matching inductance 31 is connected between the first coupling capacitor 19 and the connector, and a first matching inductance 31 is connected between the first coupling capacitor 19 and the connector, and a terminal 33 connected to the relay is connected. A second matching inductance 32 is connected, a tuning capacitor 20 is connected between the wiring conductor 26 and the ground conductor, and a tuning coil 21 (not shown) is connected between the terminal 35 and the ground conductor. Further, the second coupling capacitor 22 is connected between the connection point of the first coupling capacitor 19 and the tuning capacitor 20 and the terminal 3.
Connect between 4 and 4.

As mentioned above, the connector 24 is equipped with a specific high frequency cable that transmits an address signal of a predetermined frequency.
That is, it is connected to the CATV cable 1 via the lead-in cable 5, and the connector 25 is connected to the connector 25 as described above.
It is connected to a high frequency cable, ie, a CATV cable 2, via a lead-in cable 6. A changeover switch 11 having a relay configuration (not shown) is used to switch and connect to a connection cable 12 (see FIGS. 2 and 3).

As described above, the tuning capacitor 20 and the first and second coupling capacitors 19 and 22 are mounted on the insulating substrate 27.
By arranging them close to each other, the stray inductance becomes small, and the resonance frequency due to the stray inductance and the tuning capacitor 20 far exceeds the upper limit of the local oscillation frequency. Therefore, it is necessary to prevent the passage of the local oscillation signal. I can do it. Also, by arranging the tuning capacitor 20 and the first and second coupling capacitors 19, 22 close to each other, the first coupling capacitor 19 is located farther from the connector 24 and the terminal 33, but there is no space between them. is formed, so the first and second matching inductances 31 and 32 can be formed in that space. These matching inductances 31 and 32 are
The first coupling capacitor 19 is connected between the connector 24 and the terminal 33 in parallel with the connection circuit, and has the function of reducing transmission impedance and thereby preventing deterioration of matching characteristics. Matching characteristics can be improved.

The above-mentioned matching inductances 31 and 32 may be a lumped constant circuit such as a coil or a distributed constant circuit such as a strip line.
It can be arbitrarily selected in consideration of the above configuration, etc.

Effects of the invention As explained above, the present invention has the advantage that the insulating substrate 27
A tuning capacitor 20 and a tuning coil 21 forming a tuning circuit are connected between the wiring conductor 26 formed above and the ground conductor, and one ends of the first and second coupling capacitors 19 and 22 are connected via the wiring conductor 26. is connected to the tuning circuit in close proximity to the tuning capacitor 20, and the other end of the first coupling capacitor 19 is connected to a specific high frequency cable, in the embodiment connector 24, via a first matching inductance 31. ,
In addition, it is connected to the changeover switch 11 via a second matching inductance 32, and the other end of the second coupling capacitor 22 is connected to a connection cable 16, which outputs a signal of a predetermined frequency, that is, an address signal, to a terminal 34 in the embodiment. The tuning capacitor 20 and the first and second coupling capacitors 19 and 22
By arranging and connecting them in close proximity, the stray inductance becomes small, and the resonance frequency due to the tuning capacitor 20 and the stray inductance becomes significantly larger than the local oscillation frequency, so leakage of the local oscillation signal can be prevented. . In other words, interference with other receivers can be prevented. Also the first
By providing the second matching inductances 31 and 32, it is possible to prevent the impedance of the retracting tap from decreasing, thereby preventing the matching characteristics from deteriorating. Therefore, there is an advantage that switching of a plurality of high frequency cables and branching of a signal of a predetermined frequency such as an address signal in a CATV system etc. can be realized without adversely affecting other receiving devices.

[Brief explanation of the drawing]

Figure 1 shows multiple CATV cables installed.
An explanatory diagram of the CATV system. Figure 2 is a block diagram of the main parts of the CATV converter. Figure 3 is a circuit diagram of the selector switch and retracting tap. Figure 4 is a schematic perspective view of the circuit configuration shown in Figure 3 on an insulating board. 5 is an equivalent circuit of the retracting tap portion, and FIG. 6 is a schematic perspective view of the main part of the embodiment of the present invention. 11 is a changeover switch, 12 and 16 are connection cables, 19 and 22 are coupling capacitors, 20 is a tuning capacitor, 21 is a tuning coil, 24 and 25 are connectors, 26 is a wiring conductor, 27 is an insulating board, 31,
32 is a matching inductance, and 33, 34, and 35 are terminals.

Claims (1)

[Scope of utility model registration request] A changeover switch for switching high frequency signals transmitted by a plurality of high frequency cables, and a retracting tap consisting of a tuning circuit and a coupling capacitor tuned to a signal of a predetermined frequency transmitted by a specific high frequency cable among the plurality of high frequency cables. In the high frequency signal switching device having the above, a tuning capacitor and a tuning coil constituting the tuning circuit are connected between a wiring conductor formed on an insulating substrate and a ground conductor, and a first and a first tuning coil are connected through the wiring conductor. one end of the second coupling capacitor is connected to the tuning circuit in close proximity to the tuning capacitor, the other end of the first coupling capacitor is connected to the specific high frequency cable via a first matching inductance, and Second
A high frequency signal switching device, characterized in that the second coupling capacitor is connected to the changeover switch via a matching inductance, and the other end of the second coupling capacitor is connected to a connection cable that branches and outputs a signal of a predetermined frequency.